The following account of the prior art relates to one of the areas of application of the present disclosure, hearing aids.
When a hearing aid user takes off the hearing aids, it becomes more difficult for him or her to hear important alarms, e.g.:                In the home: Door bells, phone ringing, alarm clock, smoke or fire alarm.        In the traffic: Sirens from ambulance or fire engine, horns beeping.        
Today, solutions exist where a hearing impaired person can get a loud acoustical alarm, a visual flash or a vibration on the pocket that is connected to the ordinary alarm (doorbell, phone, smoke alarm, etc.).
U.S. Pat. No. 7,522,739 describes an automatic (e.g. temperature based) on/off switch in a hearing aid. WO 2008/055960 A1 describes an alarm system for detecting en alarm state and for alarming a user of a cochlear implant- (CI-) type hearing aid even if the normal control device for the hearing aid is inactive. US 2009/0076816 A1 describes a hearing aid system comprising a handheld device with a display for visually indicating different (otherwise acoustically indicated) events (e.g. telephone calls, alarms, etc.), so that the user thereby is alerted to the event in addition to the normal acoustic indication. US 2009/0010466 A1 describes a hearing aid system comprising a portable device, which can detect a number of specific types of sound (e.g. traffic noise, a door bell, alarms, etc.) and give the user corresponding alarms via the hearing aid. WO 2008/067638 A1 describes a hearing aid system comprising a portable unit, which can detect sound signals (e.g. alarms) in the environment of a user. When an alarm has been detected, the unit vibrates and a corresponding message is shown in a display. The user can then call for help via the portable unit.